Liner hangers have long been used in petroleum recovery operations to structurally interconnect a lower end of a large diameter tubular, such as a casing string, to a comparatively smaller diameter tubular, such as a liner. In a typical application, the casing string is cemented in place in the well bore, and the well operator seeks to suspend a smaller diameter liner concentrically within the well bore from the lower end of the casing string.
A liner may be run into the well bore from a work string, and the liner then structurally interconnected with the lower end of the casing string by a liner hanger. In a typical application, cement or another fluid may be subsequently pumped downhole through the structurally interconnected liner. Fluid may thereafter be forced upward in the annulus between the liner and the well bore. Accordingly, the liner hanger, which is structurally spaced in the annulus between the lower end of the casing and upper end of the liner, creates a restriction to this upward flow of cement or other fluid.
While various mechanisms have been used to set a liner hanger for structurally interconnection with a casing, hydraulically set liners have a significant advantage over other types of hanger setting mechanisms. Conventional liner hangers thus include a sleeve-shaped piston that moves axially with respect to the liner hanger body. In a typical application, the fluid pressure within the well bore and thus within the liner hanger body may be selectively increased until the hydraulic force supplied to the sleeve-shaped piston shears a pin, which then allows the piston to move axially to the enable camming surfaces to force the slips on the liner hanger into biting engagement with the casing.
Those skilled in the art of designing liner hangers recognize that, in many applications, the annulus between the casing and the liner may be relatively thin. The radial thickness of the liner hanger body that houses the sleeve-shaped piston accordingly is limited. An increase in the thickness of the liner hanger body is desirable in order to obtain a high pressure rating for the liner hanger, thereby allowing a higher biting force to be applied between the slips and the casing without risking rupture of the liner hanger. On the other hand, a decrease in the radial thickness of the liner hanger body is desired to minimize the flow restriction in the annulus between the casing and the liner. Accordingly, the design of prior art liner hangers has involved a balancing of an acceptable flow restriction created by the liner hanger with a desired maximum pressure rating for the liner hanger.
Another problem with many types of liner hangers is that the slips are not structurally prevented from prematurely moving radially outward. In most applications, this is not a problem since a force is not generated that would cause outward movement of the slips before the fluid pressure was intentionally increased to set the liner hanger, as explained above. In some applications, however, it is desirable to rotate the work string and thus the liner hanger while lowering the liner within a deviated well. This rotation of the liner and the hanger creates a centrifugal force that tends to force the slips radially outward before intentionally setting the liner hanger. This premature radially outward movement of the slips dulls the slip teeth due to the rotating engagement of the slip teeth with the casing. A few prior art liner hangers do, however, effectively prevent this premature radial outward movement of the hanger slips.
The disadvantages of the prior art are overcome by the present invention, and improved techniques are hereinafter disclosed for forming a hydraulically set liner hanger, and for structurally interconnecting a liner hanger with a casing. According to this invention the liner hanger may obtain a high pressure rating while still minimizing the flow restriction created by the liner hanger.